The use of various thickening agents to provide increased body and viscosity to latex compositions is well known. These thickening agents include natural gums, soluble cellulose derivatives, and a variety of high molecular weight synthetic polymers such as the sodium polyacrylate thickeners.
To obtain more economical latex compositions and provide desired viscosity and adhesive character, it is known in the art that 10 to 20% by weight of starch based on latex polymer solids may be used in latex formulations. However, the use of gelatinized or pregelatinized starches has certain drawbacks due to rheological effects which occur on aging. Starch pastes are exceedingly labile to shearing and hydrolyzing influences during processing and also in the latex compositions.
It is also known to use substantially non-birefringent, cold water swelling, granular starch products of natural and unmodified starch in latex compositions for purposes of increasing viscosity and improving the coating characteristics of the latex compositions. These starch products are substantially non-birefringent, cold water swelling, starch products having a moisture content below about 20% by weight and characterized as having a viscosity from about 150 to about 650 centipoise at 10 percent solids after being dispersed in water at 1500 rpm for 2 minutes.
Although the foregoing compositions have proved quite adequate in providing increased thickness and body of latex compositions, these compositions have not been used for replacement of latex polymer. Thus, these prior art compositions have been directed primarily toward obtaining the properties of increased thickness and viscosity rather than as an economical replacement for the petroleum derived ingredients of such latex compositions. It is the latter use which currently has become so important as the attention of the industry becomes focused upon the use of renewable resources as a substitute for limited petroleum reserves. Although starch products having thin-boiling, free-flowing characteristics have been known, for example see U.S. Pat. No. 3,067,064, it is believed that their use as a thickener in latex compositions has not been suggested, nor has their use as a latex replacement been suggested or taught in the prior art.
This invention provides novel and improved latex compositions wherein a partially swollen starch, having free-flowing, thin-boiling characteristics, is employed as a replacement for the latex polymer itself. These compositions have been found to be particularly suitable for use in the manufacture of carpet backing adhesives and employ novel pretreated starch compositions as partial replacement for styrene-butadiene (SBR) latex in such carpet-backing applications. As will be shown more fully hereafter, the novel modified starch compositions of this invention and the novel latex compositions produced therewith unexpectedly demonstrate superlative formulation properties for application in the manufacture of textile laminating compositions such as carpet backing. These properties are achieved without the necessity of having to employ a ternary mixture of modified starch, urea, and borax as is disclosed, for example, in U.S. Pat. No. 3,779,857.